SATURDAY PM, 3RD UPDATE: My sources say everything is staying pretty much as forecast, with the only question whether anything will get a bump from Father’s Day. Summer 2012 is clearly suffering a serious case of seasickness due to the constant up and down, up and down, motion of the North American box office. After the tsunami that was Marvel’s The Avengers, five major studio movies disappointed. “One movie this summer has made any money. And a number have lost a fortune,” one studio mogul maintains to me. Then DreamWorks Animation’s Madagascar 3 and Fox’s Prometheus performed better than expected and are still easily holding #1 and #2 their second weekends with $35M (-42%) and $21M (-59%) respectively. (Though the Ridley Scott scifi thriller dropped a whopping -73% Friday to Friday because of all those gaping plot holes.)

Contrast that with this weekend’s newcomers which each should have earned over $20M because of their star power. But New Line/Warner Bros’ Rock Of Ages (3,470 theaters) fell to earth with a thud. Which Hollywood expected because the pic had been tracking poorly for weeks (and even went down at one point week to week). The studio felt the 1980s period piece was a hard sell to younger moviegoers. I suspect the problem was casting. Russell Brand has been repellant to moviegoers, while Tom Cruise as iconic rocker proved just too incredulous for audiences. The PG-13 musical is looking to open to only $15M this weekend after taking in just $5.3M Friday and $5.4M Saturday. Given that the pic was based on the Broadway warbler, it did worse than the studio expected and far worse than Mamma Mia which with the same pedigree opened to $27M. Warner Bros was holding out hope for this $75M-budget pic, thinking that a good CinemaScore could generate great word of mouth and therefore great legs for the film. It didn’t materialize: audiences only gave Rock Of Ages a mediocre ‘B’. There’s just no way to save this s(t)inker with hack director Adam Shankman at the helm: in fact, weekend gross may fall below $15M by Monday.

Columbia/Sony’s That’s My Boy (3,030 theaters) starring Adam Sandler also was bottoming. It will hurt further that audiences only gave it a ‘B-‘ CinemaScore. (“But ‘B’s with everybody under 50,” a Sony exec emails me.) Hollywood didn’t expect Sandler to attract his usual family friendly audience with an ‘R’ rating. But an actor who reliably takes in $30M to $40M every opening weekend and then dropping to $13M after grossing only $4.5M Friday and $4.8M Saturday can’t go unchastized. Especially if he hurt his brand with his most recent pic, that execrable flop Jack & Jill. (How much you wanna bet Andy Samberg is rethinking that SNL exit now?) No one will be surprised if weekend gross falls below $13M by Monday.

I’m working on the autopsy reports. Overall moviegoing this weekend may be as dismal as $125M, which is -15% even compared to last year when Green Lantern bombed. Here are the Top Ten based on weekend estimates: